When dams fail: protecting Minnesotans from a catastrophic collapse

By Matt Doll – Minnesota Environmental Partnership

In the wake of the tragic collapse of a Brazilian mining waste dam that killed more than 100 people and displaced thousands more, observers around the world have asked, “Could it happen here?” While it is evident that lax enforcement and managerial malfeasance contributed greatly to this disaster, it is entirely possible that a similarly large flood of mine waste could strike in Minnesota.

The PolyMet mine dam proposal – which was recently permitted by The Department of Natural Resources –  uses the same kind of tailings waste dam construction as the Vale mine that failed this week.  Though already permitted, the Department of Natural Resources has the ability to revisit that decision in light of this disaster to make sure Minnesotans are protected.

The hazards when flooding mixes with mines

The deadliest mining disaster in Minnesota’s history to date was the Milford Mine flood in 1924, in which a cave-in at a manganese mine caused the waters of Foley Lake to rush into the 200-foot-deep pit, killing 41 workers. This tragedy shocked Minnesota, but it wasn’t completely unanticipated – according to a survivor, the company mining engineer warned management repeatedly that the mine’s proximity to the lake was unsafe. Fortunately, the flood – and the manganese ore, which can cause neurological diseases if present in drinking water – was relatively contained within the mine.

The proposed PolyMet mine is a different story. While mining today tends to enjoy the benefits of safer technology, PolyMet carries its own spill risk. The current proposal calls for the mine tailings waste, which includes compounds that release high levels of toxic acid into water, to be kept behind a 40-year-old earthen upstream dam, similar in construction to the failed dam in Brazil. This type of dam is obsolete technology, with three catastrophic failures in just the last 5 years. The dry stacking of mine tailings is a far safer waste storage method, but would require more work and investment from PolyMet, which has refused to seriously consider using it.

The dam would need to be maintained indefinitely (read: hundreds of years) but that’s no guarantee it would hold forever against floods and erosion. One engineer hired to evaluate the project said that “a lake on top of a pile of sand is inherently unstable, and irresponsible.”

A strong enough flood (an increasing risk as climate change boosts rainfall in Minnesota) would cause the dam to fail, spilling toxic waste not only into a mine shaft, but into the St. Louis River watershed, which feeds into Lake Superior and on which thousands of people rely. This would not be an outlier in the history of sulfide ore mines in the United States – no such mine has ever operated in this country without polluting the surrounding water and habitat.

Seeking to stave off catastrophic consequences

Minnesotans are determined that a disaster on the scale of the tragedy in Brazil should not be replicated in our state. On January 31^st, the Fond du Lac band of Lake Superior Chippewa and several of MEP’s partnering organizations called on the DNR to revisit the permits for the dam construction in light of this catastrophe.

Said Kathryn Hoffman of the Minnesota Center for Environmental Advocacy (MCEA): “The disaster in Brazil has shown that PolyMet’s plan to store sulfide mine waste tailings behind an unsafe dam begun in the 1950s is a risk that Minnesota can’t bear.” MCEA and several other MEP member organizations are also continuing with a lawsuit to block PolyMet’s land exchange with the federal government on the grounds that it shortchanges the public interest.

We urge concerned Minnesotans to share their views as well. By asking Governor Walz and DNR Commissioner Sarah Strommen to reconsider the dam permit, we can help protect Minnesota from a dam we can’t afford and a catastrophe we hope never to face.